The present invention relates to improved low-quality particulates, to methods for improving low-quality particulates, and to methods of using improved low-quality particulates in hydraulic fracturing, frac packing, and gravel packing treatments.
Hydrocarbon-producing wells are often stimulated by hydraulic fracturing treatments. In hydraulic fracturing treatments, a viscous fracturing fluid is pumped into a producing zone at a rate and pressure such that the subterranean formation breaks down and one or more fractures are formed in the zone. Particulate solids, such as graded sand, which are often referred to as “proppant” are suspended in a portion of the fracturing fluid and then deposited in the fractures when the fracturing fluid is converted to a thin fluid to be returned to the surface. These particulates serve, inter alia, to prevent the fractures from fully closing so that conductive channels are formed through which produced hydrocarbons can flow.
Hydrocarbon-producing wells may also undergo gravel packing treatments to reduce the migration of unconsolidated formation particulates into the well bore. In gravel packing operations, particulates, often referred to in the art as gravel, are carried to a well bore in a subterranean producing zone by a servicing fluid that acts as a gravel carrier fluid. That is, the particulates are suspended in a carrier fluid, which may be and usually is viscosified, and the carrier fluid is pumped into a well bore in which the gravel pack is to be placed. As the particulates are placed in or near the zone, the carrier fluid leaks off into the subterranean zone and/or is returned to the surface. The resultant gravel pack acts as a sort of filter to prevent the production of the formation solids with the produced fluids. Traditional gravel pack operations involve placing a gravel pack screen in the well bore before packing the surrounding annulus between the screen and the well bore with gravel. The gravel pack screen is generally a filter assembly used to support and retain the gravel placed during the gravel pack operation. A wide range of sizes and screen configurations is available to suit the characteristics of a well bore, the production fluid, and any particulates in the subterranean formation. Gravel packs are used, among other reasons, to stabilize the formation while causing minimal impairment to well productivity.
In some situations, hydraulic fracturing and gravel packing operations may be combined into a single treatment. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment ends in a screen-out condition, creating an annular gravel pack between the screen and casing. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
To prevent the subsequent flow-back of proppant, gravel, and other particulates with the produced fluids, a portion of the particulates introduced into a subterranean formation may be coated with a curable resin that may facilitate the consolidation the particulates in the fracture. A variety of resin-coated proppant materials have been used in modern hydraulic fracturing treatments. These include graded natural materials, such as sand or nut shells, or constructed materials, such as bauxite, ceramic materials, glass materials, polymer beads, composite particles, and the like. Most common of these are high-quality graded natural sands, such as Ottawa sand. Unfortunately, high quality sands such as these are in short supply and are becoming increasingly costly. Lower quality sands could be used; however, proppant packs composed of lower-quality sands (even those coated with curable resins using traditional coating techniques) often contain large amounts of fines, and typically have lower conductivities and are generally more susceptible to proppant crushing, making them inadequate for most fracturing treatments.